Quantum dots are nanometric scale particles, or “nanoparticles” that show quantum confinement effects. In the case of semiconductor nanoparticles having spatial dimensions less than the exciton Bohr radium, the quantum confinement effect manifests itself in the form of size-dependent tunable band gaps and, consequently, tunable light absorption and emission properties.
To exploit the tunable properties, semiconductor quantum dots are incorporated into devices, such as photovoltaic cells and light emitting diodes, typically in the form of films having suitable electronic and optical coupling with the device and the outside world. Semiconductor quantum dots have been incorporated into inorganic films for use in a variety of devices. For example, published U.S. Patent Application US 2005/010747 describes nanocrystal-polymer complexes dispersed in a titania matrix for use in photoluminescent devices. Unfortunately, the large size of the amphiphilic polymers of the complex make it difficult to achieve high nanoparticle loadings in the matrix. In addition, the amphiphilic polymer and/or any capping ligands on the nanoparticles within the matrix may act as an insulating layer, rendering the material unsuitable for applications where such an insulating layer would be undesirable. Organo-Silane-capped Group II-IV quantum dots in a silicate film for use in light emitting devices are described in U.S. Pat. No. 6,869,864. In addition, CdS and PbS quantum dots have been incorporated into silica-titania films. See, for example, Martucci, et al., J. Appl. Phys., 86, 79 (1999). However, none of the above-cited references teach films containing Group IV semiconductor nanoparticles in an oxide matrix that are suitable for use in photoactive devices, such as photovoltaic devices. Nor do the references teach methods suitable for forming such films.